Up to now, methods and devices for detecting fetal movement frequencies are known which detect the number of fetal movements in a fixed time period in order to grasp whether a fetus in the uterus of the mother's body is growing smoothly.
As such methods and devices for detecting fetal movement frequencies, various kinds of methods and devices have been proposed and implemented which are configured so that the mother pushes a button when feeling a fetal movement or so that a fetal movement sensor for detecting fetal movements is attached on the mother's abdomen in order to determine whether there is a fetal movement on the basis of the output signal from the fetal movement sensor.
For example, in Japanese Unexamined Patent Publication No. 11-89832 (Patent Document 1), a fetal movement measuring instrument is disclosed which is configured so that fetal movements are detected using a thin-film piezoelectric sensor, and it is determined that the fetus is healthy if a predetermined number (10) or more of fetal movements are detected within a fixed period of time (two hours) or it is determined that the fetus is in a dangerous condition if the number of fetal movements in a fixed period of time (8 hours) is less than a predetermined number (10).
However, there are differences among fetuses, and fetal movements include those which occur two or more times in a fixed cycle such as “hiccups”, those which occurs singly such as “kicks” or “rolls”, and the like, so that detecting only fetal movement frequencies as described above is not sufficient for determining the state of health of the fetus.
Furthermore, no movement a fetus gives in a fixed period of time can not necessarily decide that the fetus is in a dangerous condition. For example, “Hideki Kawaguchi, et. al., “Fetal Asphyxia and Its Countermeasure”, Sanfujinkairyo (in Japanese), 1999 Supplement. (Vol. 78), pp. 224-228” (Non-patent Document 1) shows data indicating that a healthy fetus gave continuously no movement for a time as long as 75 minutes.
In addition, high sensitivity employed for detecting movements of a fetus in the uterus of the mother's body by signals from the mother's abdomen, catches a signal from the mother by her movement such as breath to count as one component of fetal movement, thereby to count a number beyond real fetal movements, resulting in a risk of missing that the fetus has a reduced number in fetal movement.
Patent Document 1: Japanese Unexamined Patent Publication No. 11-89832
Non-patent Document 1: Hideki Kawaguchi, et. al., “Fetal Asphyxia and Its Countermeasure”, Sanfujinkairyo (in Japanese), 1999 Supplement. (Vol. 78), pp. 224-228